What Happens If You Mix Foo Fighters, Zac Brown And Black Sabbath? [VIDEO]

C'mon, admit it. You've always wondered that haven't you?  Read on for the answer!

Last night on Letterman, the Foo Fighters payed tribute to one of their idols - Black Sabbath - with Zac Brown handling the vocals!  And they totally nail it!

If Zac ever gets tired of his country gig, I think he could handle himself in the rock world! Foo Fighters meanwhile are gearing up for the release of their new disc "Sonic Highways" which drops November 11th.

They will end their run as as Letterman's "house band" Friday night, which is the same night their HBO special "Sonic Highways" premieres!

In addition to performing and talking about their new projects, Dave Grohl also caught us up on his home life being Dad to three future rocker-ettes.  Not easy when one of them is a little gangsta'!